Image Diff is a windows application that allows you to visually compare two copies of an image contained in a Subversion Repository using Tortoise SVN.
It works by Tortoise SVN passing the filename parameters of the base and modified versions of the image to the Image Diff application which loads the files into two tabs which you can then switch between to visually look for differences. It's not rocket science but works for me.
It should work with image filetypes of bmp, gif, jpg, png, ico, emf and wmf. but have only tested jpg and gif